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Spark ignited engines with direct injection (DISI) in fuel stratified mode promise an increase in efficiency mainly due to reduced pumping losses at part load. However, the need for expensive lean NOx catalysts may reduce this advantage. Therefore, a Bowl-Prechamber-Ignition (BPI) concept with flame jet ignition was developed to ignite premixed lean mixtures in DISI engines. It is characterised by a combination of a prechamber spark plug and a piston bowl. An important feature of the concept is its dual injection strategy. A pre injection in the inlet stroke produces a homogeneous lean mixture with an air fuel ratio of λ = 1.5 to λ = 1.7. A second injection with a small quantity of fuel is directed towards the piston bowl during the compression stroke. The enriched air fuel mixture of the piston bowl is transported by the pressure difference between main combustion chamber and prechamber into the prechamber.

To operate gasoline direct injection engines at part load and in stratified mode the mixture formation has to fulfil several requirements. The complexity of this process requires - regarding a suitable mixture transportation and vaporisation of the fuel - an adjusted design of the combustion chamber and the intake ports to reliably place an ignitable mixture at ignition timing near the spark plug at any speed and load. Due to the inhomogeneous mixture distribution during stratified operation, the first combustion period is very sensitive to cycle-to-cycle variations. A reproducible mixture movement with high kinetic energy is necessary for stable engine operation with low fluctuations in the combustion process. Because of the high relevance of these facts, the effects of an adjustable air guiding system in the inlet manifold on in-cylinder flow, ignition and combustion using optical measurement techniques were investigated.